This invention relates to a downhole steam generator for use in the injection of steam into a hydrocarbon or other mineral containing formation to reduce said mineral's viscosity and provide energy to drive said mineral from the formation.
A reference believed to be relevant to the present invention is U.S. Pat. No. 3,420,300 issued to the present application on Jan. 7, 1969. That patent teaches the use of a catalytic heater in a borehole for heating a subsurface formation.
Hydrocarbon materials can be removed from a hydrocarbon bearing subterranean formation by the injection of steam. In this method of recovery steam is injected into the formation to reduce the hydrocarbon viscosity and to provide a driving medium to force the hydrocarbon to a producing well bore. The producing well bore may be a well, or wells, adjacent the steam injection well or the injection well may be used as the producing well in which case the steam injection would be terminated during the production of hydrocarbons. This latter method of operation is called huff and puff while the former is called steam drive. The recovery of hydrocarbons is accelerated by the reduction of its viscosity such that it will flow more readily to the producing well bores. Recovery of hydrocarbons is also enhanced by the steam distillation of fractions of the hydrocarbons which are moved toward the producing wells.
In carrying out this recovery method, it is necessary to force steam into the formation with sufficient heat energy to substantially heat the formation and hydrocarbons therein. The generation of steam usually has been by the usage of surface boilers with insulated steam lines running from the boiler to the injection wells. Steam passes through tubing within the injection well bore to the hydrocarbon bearing formation where it enters to heat the formation. Many such steam recovery operations now exist, however, the depth to which this method is applicable is generally less than 3000 feet. The heat loss from the steam containing tubing passing through several hundreds of feet of barren formations above the hydrocarbon formation is excessive. At great depth the steam would all be condensed to water and finally cooled to essentially the temperature of the hydrocarbon bearing formation. Thus the injection of steam from the surface to even moderate depths of 3000 to 5000 feet is ineffective in recovering oil by this method. Some attempts have been made to construct downhole steam generators. These have been by electrical heaters or open flame heaters. The electric downhole heaters are of limited capacity and use and are considered too expensive a means to create a sustained amount of steam energy. The open flame heaters have also been of limited capacity and difficult to control and maintain.